Scraping a living: a review of littorinid grazing

Littorinid snails are predominantly herbivorous and the versatility of their radulae enables them to feed on a variety of macroscopic and microscopic plants in a diversity of habitats. Some are selective feeders preferring some species of algae to others, and rejecting some even after a prolonged period of starvation. Different species of snail exhibit different preferences. The factors affecting the attractiveness and edibility of food plants are discussed and food value considered.Foraging behaviour of littorinids is briefly reviewed in relation to the influence of chemical cues from the algae. Littorinids appear to be able to select or reject algae without having ingested them, having perceived the plants from a distance, moving towards favoured foods (or habitat-providing plants) and away from those that it rejects. The nature of the chemical cues emitted by the algae is discussed. Temporal patterns of foraging activity show some evidence of an endogenous component which can be overridden by responses to environmental conditions. These patterns place restraints on energy intake.The structural and chemical defences used by algae against littorinid grazing are considered. The importance of polyphenolic compounds is evaluated. The effects of grazing as a selective agency and a factor influencing algal populations are discussed. There is some evidence that life history patterns are a response to grazing. The influence of external physical factors, such as salinity on grazing pressure is demonstrated.Finally, the impact of littorinid snails on intertidal communities is assessed in relation to their abundance and biogeographical distribution. The relative importance of littorinids is contrasted on shores possessing or lacking limpets.     

放牧家畜排泄物N转化研究进展

放牧家畜排泄物氮转化是草原生态系统氮循环的关键。自 2 0世纪 70年代以来 ,以提高氮利用效率和减少温室气体排放为目的的家畜排泄物氮转化的研究越来越受到人们的重视。放牧家畜排泄物氮的转化研究主要包括 3个方面 :氮的矿化、硝化与反硝化 ,氮的氨化。家畜粪氮矿化速度慢 ,持续时间长 ;尿氮矿化速度快 ,持续时间短。氮矿化与家畜排泄物 C∶ N比、木质素/氮素比、木质素含量和纤维素含量呈负相关关系 ,而与全氮含量和水溶性氮含量呈正相关 ;土壤动物和微生物可以显著促进氮的矿化过程 ;高温和相对干燥、砂质土壤较壤土和粘土有利于氮的矿化。 4～ 4 0℃氮硝化作用与温度呈正相关 ;硝化作用的底物和产物浓度、土壤溶液渗透压和氯化物浓度的增加对硝化作用有强烈的抑制效应 ;p H6 .0～ 8.0条件下硝化作用强度随着土壤p H值的升高而增加 ,而 p H值高于 8.0或低于 6 .0时硝化作用受到抑制 ;硝化作用与土壤氧气含量呈正相关关系 ,而与土壤含水量呈负相关 ;温暖湿润较干燥炎热的气候条件有利于硝化过程的进行。反硝化作用与土壤氧气浓度呈负相关关系 ,而与土壤含水量和可利用有机碳含量呈正相关 ;0～ 6 5℃反硝化作用强度随温度升高而增大 ,10～ 35℃条件下温度成为影响反硝化作用的关键因素 ;反硝化作用在     

Potential infection of grazing cattle via contaminated water: a theoretical modelling approach

Wastewater discharge and agricultural activities may pose microbial risks to natural water sources. The impact of different sources can be assessed by water quality modelling. The aim of this study was to use hydrological and hydrodynamic models to illustrate the risk of exposing grazing animals to faecal pollutants in natural water sources, using three zoonotic faecal pathogens as model microbes and fictitious pastures in Sweden as examples. Microbial contamination by manure from fertilisation and grazing was modelled by use of a hydrological model (HYPE) and a hydrodynamic model (MIKE 3 FM), and microbial contamination from human wastewater was modelled by application of both models in a backwards process. The faecal pathogens Salmonella spp., verotoxin-producing Escherichia coli O157:H7 (VTEC) and Cryptosporidium parvum were chosen as model organisms. The pathogen loads on arable land and pastures were estimated based on pathogen concentration in cattle faeces, herd prevalence and within-herd prevalence. Contamination from human wastewater discharge was simulated by estimating the number of pathogens required from a fictitious wastewater discharge to reach a concentration high enough to cause infection in cattle using the points on the fictitious pastures as their primary source of drinking water. In the scenarios for pathogens from animal sources, none of the simulated concentrations of salmonella exceeded the concentrations needed to infect adult cattle. For VTEC, most of the simulated concentrations exceeded the concentration needed to infect calves. For C. parvum, all the simulated concentrations exceeded the concentration needed to infect calves. The pathogen loads needed at the release points for human wastewater to achieve infectious doses for cattle were mostly above the potential loads of salmonella and VTEC estimated to be present in a 24-h overflow from a medium-size Swedish wastewater treatment plant, while the required pathogen loads of C. parvum at the release points were below the potential loads of C. parvum in a 24-h wastewater overflow. Most estimates in this study assume a worst-case scenario. Controlling zoonotic infections at herd level prevents environmental contamination and subsequent human exposure. The potential for infection of grazing animals with faecal pathogens has implications for keeping animals on pastures with access to natural water sources. As the infectious dose for most pathogens is more easily reached for calves than for adult animals, and young calves are also the main shedders of C. parvum, keeping young calves on pastures adjacent to natural water sources is best avoided.     

Thermal balance of cattle grazing winter range: Model development

Beef cattle grazing semi-arid foothill range of the Northern Rockies during winter may be exposed to cold temperatures and high winds while grazing pastures with low nutritional value. We refined a simple thermal balance equation to model heat exchange of free-ranging cattle. We account for the complex interactions between animal behavior and the changing natural environment by applying the components of the model to a rotating ellipsoid representing a cow at different orientations to the sun and wind. Correlation coefficients (r) between predicted standard operative temperature and measured surface temperature ranged from 0.82 on an individual basis to 0.88 on a herd average basis, indicating the model successfully quantifies heat exchanges of cattle exposed to cold conditions in the field.     

Phosphorus requirements of tropical grazing systems: the northern Australian experience

Background and aims

Extensive grazing is common on low phosphorus (P) soils in tropical areas. In this study we aimed to use experience and research results from northern Australia to investigate methods to manage low P status to efficiently raise animals without exploiting soil P resources.

Scope

Simple ??farm-gate?? P balances were calculated for four cattle breeding and growing operations. Estimated P balances were slightly negative (outputs>inputs) for extensive breeding operations (0.02 to 0.04 kg/ha/year depending on P supplementation), slightly positive for a system growing young animals with small annual P fertilizer applications, and negative for a mixed grazing-cropping enterprise. In northern tablelands pastoral environments, responses to P application have remained unchanged over the last 50 years, with >80% of paddocks remaining P limited. Liveweight gain responses to P fertilizer in most experiments have been <4 kg LWG/kg P applied as fertilizer.

Conclusions

Little or no P fertilizer is used in most grazing systems. Supplying P directly to animals as a feed supplement can economically improve animal performance and contribute to an improvement in the P balances of grazing systems. Guidelines for supplement use have been devised. Further research is required to determine the best application strategies to overcome P deficits, and the best farming systems to minimise P requirements.     

Effects of grazing on grassland soil carbon: a global review

Soils of grasslands represent a large potential reservoir for storing CO₂, but this potential likely depends on how grasslands are managed for large mammal grazing. Previous studies found both strong positive and negative grazing effects on soil organic carbon (SOC) but explanations for this variation are poorly developed. Expanding on previous reviews, we performed a multifactorial meta‐analysis of grazer effects on SOC density on 47 independent experimental contrasts from 17 studies. We explicitly tested hypotheses that grazer effects would shift from negative to positive with decreasing precipitation, increasing fineness of soil texture, transition from dominant grass species with C₃ to C₄ photosynthesis, and decreasing grazing intensity, after controlling for study duration and sampling depth. The six variables of soil texture, precipitation, grass type, grazing intensity, study duration, and sampling depth explained 85% of a large variation (±150 g m^?2 yr^?1) in grazing effects, and the best model included significant interactions between precipitation and soil texture (P = 0.002), grass type, and grazing intensity (P = 0.012), and study duration and soil sampling depth (P = 0.020). Specifically, an increase in mean annual precipitation of 600 mm resulted in a 24% decrease in grazer effect size on finer textured soils, while on sandy soils the same increase in precipitation produced a 22% increase in grazer effect on SOC. Increasing grazing intensity increased SOC by 6–7% on C₄‐dominated and C₄–C₃ mixed grasslands, but decreased SOC by an average 18% in C₃‐dominated grasslands. We discovered these patterns despite a lack of studies in natural, wildlife‐dominated ecosystems, and tropical grasslands. Our results, which suggest a future focus on why C₃ vs. C₄‐dominated grasslands differ so strongly in their response of SOC to grazing, show that grazer effects on SOC are highly context‐specific and imply that grazers in different regions might be managed differently to help mitigate greenhouse gas emissions.     

In vitro fertilization in cattle: a review

In vitro maturation and fertilization of cattle oocytes and subsequent in vitro culture of zygotes and embryos is discussed in the context of recent encouraging data. Mass production of embryos produced in this way in the future will have a great impact on animal production and animal breeding plans, for example the so-called MO-ET (multiple ovulation and embryo transfer) plan which aims at establishing nucleus breeding herds.     

Genetic disorders in beef cattle: a review

The main purpose of present review is to describe and organize autosomal recessive disorders (arachnomelia, syndactylism, osteopetrosis, dwarfism, crooked tail syndrome, muscular hyperplasia, glycogen storage disease, protoporphyria), which occur among beef cattle, and methods that can be applied to detect these defects. Prevalence of adverse alleles in beef breeds happens due to human activity—selections of favorable features, e.g. developed muscle tissue. Unfortunately, carriers of autosomal recessive diseases are often characterized by these attributes. Fast and effective identification of individuals, that may carry faulty genes, can prevent economical losses.     

Site of semen deposition in cattle: a review

The breeding of cattle using conventional artificial insemination methods involves the deposition of semen in the uterine body. However, it has been recently proposed by several authors that the site of semen deposition be changed to the uterine horns. This suggestion is based on 2 facts: the acceptance that the major preovulatory sperm reservoir may be the uterotubal junction rather than the cervical canal, and the lack of accuracy by inseminators in depositing semen. In over 50% of cases, inseminators were not sufficiently trained to deposit semen into the uterine body, so that intracervical insemination was often performed resulting in reduced fertility. The advantage of deep uterine insemination, whether bicornual or unicornual, is that it favors the deposition of semen nearer to the uterotubal junction and thus reduces the incidence of cervical deposition. This review updates the literature on the ideal site of semen deposition, including cervical, uterine body, cornual and intraperitoneal. Also analyzed are the effects of right vs. left side activity of the female reproductive tract on the optimum site of semen deposition as it affects fertilization. Finally, the question of whether the clinical training of inseminators should be reevaluated is discussed.     

Need for escape protein by grazing cattle

Grazing cattle require rumen degradable protein to meet the needs of the microbial population and rumen undegradable protein to meet the productive needs of the animal. The need for rumen degradable protein is about 130 g kg⁻¹ of digestible organic matter. However, when low-quality forage is consumed, rate of passage is reduced, microbial growth rate is reduced and conversion efficiency of microbial growth is reduced. This probably lowers the rumen degradable protein requirement. Escape protein is necessary to meet cattle requirements for growth or lactation. Microbial protein is usually adequate for animals at or near maintenance. The protein in both cool-season and warm-season grasses is highly degraded. Therefore, growing cattle and lactating cows responded to supplemental escape protein. Knowledge of the rumen degradable and undegradable protein contents of grazed forages is essential to more precisely predict animal performance and the animal response to protein supplements.     

Zooplankton grazing on Phaeocystis: a quantitative review and future challenges

The worldwide colony-forming haptophyte phytoplankton Phaeocystis spp. are key organisms in trophic and biogeochemical processes in the ocean. Many organisms from protists to fish ingest cells and/or colonies of Phaeocystis. Reports on specific mortality of Phaeocystis in natural plankton or mixed prey due to grazing by zooplankton, especially protozooplankton, are still limited. Reported feeding rates vary widely for both crustaceans and protists feeding on even the same Phaeocystis types and sizes. Quantitative analysis of available data showed that: (1) laboratory-derived crustacean grazing rates on monocultures of Phaeocystis may have been overestimated compared to feeding in natural plankton communities, and should be treated with caution; (2) formation of colonies by P. globosa appeared to reduce predation by small copepods (e.g., Acartia, Pseudocalanus, Temora and Centropages), whereas large copepods (e.g., Calanus spp.) were able to feed on colonies of Phaeocystis pouchetii; (3) physiological differences between different growth states, species, strains, cell types, and laboratory culture versus natural assemblages may explain most of the variations in reported feeding rates; (4) chemical signaling between predator and prey may be a major factor controlling grazing on Phaeocystis; (5) it is unclear to what extent different zooplankton, especially protozooplankton, feed on the different life forms of Phaeocystis in situ. To better understand the mechanisms controlling zooplankton grazing in situ, future studies should aim at quantifying specific feeding rates on different Phaeocystis species, strains, cell types, prey sizes and growth states, and account for chemical signaling between the predator and prey. Recently developed molecular tools are promising approaches to achieve this goal in the future.     

Spatial pattern changes of grazing cattle population I

A cattle population presents three spatial patterns according to their behaviour. These patterns are as follows: the random spatial pattern which occurs when the cattle move during grazing (feeding), the aggregated spatial pattern which occurs when they rest, and the regular or quasi-regular spatial pattern which occurs when they separate into two or more subgroups. In this study, these three states of behaviour were represented by a mathematical model, and a method to test the pattern statistically was derived.     

Zinc nutrition in rice production systems: a review

Background

Zinc (Zn) deficiency is one of the important abiotic factors limiting rice productivity worldwide and also a widespread nutritional disorder affecting human health. Given that rice is a staple for populations in many countries, studies of Zn dynamics and management in rice soils is of great importance.

Scope

Changing climate is forcing the growers to switch from conventional rice transplanting in flooded soils to water-saving cultivation, including aerobic rice culture and alternate wetting and drying system. As soil properties are changed with altered soil and water management, which is likely to affect Zn solubility and plant availability and should be considered before Zn management in rice. In this review, we critically appraise the role of Zn in plant biology and its dynamics in soil and rice production systems. Strategies and options to improve Zn uptake and partitioning efficiency in rice by using agronomic, breeding and biotechnological tools are also discussed.

Conclusions

Although soil application of inorganic Zn fertilizers is widely used, organic and chelated sources are better from economic and environmental perspectives. Use of other methods of Zn application (such as seed treatment, foliar application etc., in association with mycorrhizal fungi) may improve Zn-use efficiency in rice. Conventional breeding together with modern genomic and biotechnological tools may result in development of Zn-efficient rice genotypes that should be used in conjunction with judicious fertilization to optimize rice yield and grain Zn content.     

Heritability estimates for carcass traits of cattle: a review

We present estimates of heritability for carcass traits of cattle published in the scientific literature. Seventy-two papers published from 1962 to 2004, which reported estimates of heritability for carcass traits, were reviewed. The unweighted means of estimates of heritability for 14 carcass traits by slaughter end point (age, weight, and fat depth) were calculated. Among the three end points, carcass weight, backfat thickness, longissimus muscle area, and marbling score were the carcass traits with the most estimates of heritability (56 相似文献   

Long-term changes of salt marsh communities by cattle grazing

Over a period of 9 years a grazing experiment was carried out in the mainland salt marsh of the Leybucht (Niedersachsen) with three stocking rates, namely, 0.5 ha^-1, 1 ha^-1, and 2 cattle ha^-1. These were also compared with an abandoned area. The results are based on sampling of the invertebrates in 1980, 1981, 1982, and 1988, and of the vegetation in 1980 and 1988. The rate of sedimentation is highest in the Puccinellia maritima-zone and decreases with the increase of stocking rates. The Elymus pycnanthus vegetation type becomes dominant in the higher salt marsh in the abandoned site. The canopy height decreases with increasing stocking rate, whereas a gradient in the structure of the vegetation develops with the lowest stocking rate. The population densities, the species-richness and the community diversity of invertebrates increases after the cessation of grazing. The high rate of sedimentation in the abandoned site promotes the immigration of species from higher salt marsh levels and adjacent grasslands, and eventually halotopophilous species and communities may disappear. On the other hand grazing reduces numerous species living both in or on upper parts of the vegetation or being sensitive to trampling by cattle. The community structure shows that the salt marsh ecosystem changed from a food web dominated by plant feeding animals to a food web dominated by animals foraging on detritus. The salt marsh management has to be differentiated into both ungrazed and lightly grazed areas (each 50%) or an overall grazing in large areas with less than 0.5 cattle ha^-1.     

The effects of cattle grazing on plant-pollinator communities in a fragmented Mediterranean landscape

The main aims of this study were to assess grazing impacts on bee communities in fragmented mediterranean shrubland (phrygana) and woodland habitats that also experience frequent wildfires, and to explain the mechanisms by which these impacts occur. Fieldwork was carried out in 1999 and 2000 on Mount Carmel, in northern Israel, a known hot-spot for bee diversity. Habitats with a range of post-burn ages and varying intensities of cattle grazing were surveyed by transect recording, grazing levels, and the diversity and abundance of both flowers and bees were measured. The species richness of both bees and flowers were highest at moderate to high grazing intensities, and path-analysis indicated that the effects of both grazing and fire on bee diversity were mediated mainly through changes in flower diversity, herb flowers being more important than shrubs. The abundance of bees increased with intensified grazing pressure even at the highest levels surveyed. Surprisingly though, changes in bee abundance at high grazing levels were not caused directly by changes in flower cover. The variation in bee abundance may have been due to higher numbers of solitary bees from the family Halictidae in grazed sites, where compacted ground (nesting resource) and composites (forage resource) were abundant. The effects of grazing on plants were clearest in the intermediate-aged sites, where cattle inhibited the growth of some of the dominant shrubs, creating or maintaining more open patches where light-demanding herbs could grow, thus allowing a diverse flora to develop. Overall, bee communities benefit from a relatively high level of grazing in phrygana. Although bee and flower diversity may decrease under very heavy grazing, the present levels of grazing on Mount Carmel appear to have only beneficial effects on the bee community.